Method of obtaining a modified image of a specimen

Abstract

A method of obtaining an image of a specimen in a scanning electron microscope, the image being modified by way of compensating for detector afterglow effects, is provided. The method includes: acquiring first image data, the first image data including a plurality of pixels having values representing monitored electrons emitted from the specimen, at a plurality of locations within a region thereof as a result of an electron beam of the scanning electron microscope impinging upon the plurality of locations, and incident upon a scintillator member of an electron backscatter diffraction, EBSD, detector, and generating a modified image including a plurality of pixels each having a value calculated based on the value of a corresponding pixel of the first image data and an afterglow model representative of a luminescence persistence characteristic of the scintillator member. A system and computer program product are also provided.

1 . A method of obtaining a modified image of a specimen in a scanning electron microscope, the method comprising:
 acquiring first image data, the first image data comprising a plurality of pixels having values representing monitored electrons emitted from the specimen, at a plurality of locations within a region thereof as a result of an electron beam of the scanning electron microscope impinging upon the plurality of locations, and incident upon a scintillator member of an electron backscatter diffraction, EBSD, detector; and   generating a modified image comprising a plurality of pixels each having a value calculated based on the value of a corresponding pixel of the first image data and an afterglow model representative of a luminescence persistence characteristic of the scintillator member.   
     
     
         2 . The A method according to  claim 1 , wherein the first image data comprises a first image comprising the plurality of pixels, and wherein each pixel of the plurality of pixels corresponds to, and has a value representing the monitored electrons incident on a first region of the scintillator member and emitted from, a location of the plurality of locations. 
     
     
         3 . The method according to  claim 2 , wherein the first image data further comprises a second image comprising a second plurality of pixels, and wherein each pixel of the second plurality of pixels corresponds to, and has a value representing the monitored electrons incident on a second region of the scintillator member and emitted from, a location of the plurality of locations, wherein the first and second regions of the scintillator member are different. 
     
     
         4 . The method according to  claim 3 , wherein the first image data comprises a plurality of images representing the monitored electrons incident on a respective plurality of regions of the scintillator member, and wherein the method further comprises:
 providing a respective afterglow model for each of the plurality of regions; and   generating, for each of the plurality of regions, a respective modified image based on the corresponding image and the respective afterglow model.   
     
     
         5 . The method according to  claim 1 , wherein the first image data comprises a set of electron backscatter diffraction pattern, EBSP, images, each comprising a respective subset of the plurality of pixels having values representing a respective subset of the monitored electrons emitted from the specimen at a respective location of the plurality of locations,
 wherein the method comprises generating, for each of the set of EBSP images, a respective modified image comprising a plurality of pixels, each pixel having a value calculated based on the value of a corresponding pixel of the EBSP image and the afterglow model.   
     
     
         6 . The method according to  claim 1 , wherein the generating of the modified image comprises, for each of the plurality of pixels thereof:
 obtaining scintillator state data representative of energization, at the start of a monitoring period, of the scintillator member by electrons incident on the scintillator member prior to the monitoring period, wherein the monitoring period is the period of time during which the electrons emitted from the specimen at the location corresponding to the pixel are monitored so as to obtain the value of the corresponding pixel of the first image data; and   calculating the value of the pixel in accordance with the scintillator state data.   
     
     
         7 . The method according to  claim 6 , wherein the obtained scintillator state data is representative of electrons incident upon the scintillator member and emitted from the specimen at each of a set of one or more calibration locations as a result of the electron beam impinging upon the set of calibration locations prior to impinging on the location corresponding to that one of the plurality of pixels. 
     
     
         8 . The method according to  claim 7 , wherein each of the calibration locations is different from each of the plurality of locations. 
     
     
         9 . The method according to  claim 7 , wherein the first image data comprises pixel values obtained by way of the electron beam traversing the region of the specimen according to a raster pattern; and
 wherein the set of calibration locations comprises one or more locations along a flyback path comprised by the raster pattern.   
     
     
         10 . The method according to  claim 7 , wherein the scintillator state data is derived from data obtained from the EBSD detector while the electron beam is being caused to impinge upon a first calibration location for a calibration time period; and
 wherein the calibration time period is immediately prior to a monitoring period for a pixel of the first image data.   
     
     
         11 . The method according to  claim 10 , wherein the first calibration location is a first location, of the plurality of locations, on which the electron beam impinges during acquiring the first image data; and
 wherein the calibration time period is greater than or equal to a luminescence decay time period of the scintillator member.   
     
     
         12 . The method according to  claim 11 ,
 wherein the scintillator state data further comprises data derived from the EBSD detector while the electron beam is being caused to impinge upon one or more further calibration locations for one or more respective calibration time periods, wherein each calibration time period is immediately prior to a monitoring period for a respective pixel of the first image data;   wherein each further calibration location is a respective first location, of the plurality of locations, on which the electron beam impinges during acquiring a respective portion of the first image data; and   wherein, for each further calibration location, the respective calibration time period is greater than or equal to a luminescence decay time period of the scintillator member.   
     
     
         13 . The method according  claim 6 , wherein the scintillator state data is obtained in accordance with the first image data and beam path data indicative of a path on the specimen traversed by the beam. 
     
     
         14 . The method according to  claim 13 , wherein the obtaining of the scintillator state data comprises calculating an estimated energization, at the start of a monitoring period, of the scintillator member by electrons emitted from the specimen as a result of the electron beam impinging on the beam path and incident on the scintillator member prior to the monitoring period, based on, for each of one or more pixels of the first image data, the pixel value and a positional relationship between the corresponding location and the beam path. 
     
     
         15 . The method according to  claim 1 , the method further comprising:
 causing the electron beam of the scanning electron microscope to impinge upon the plurality of locations within the region of the specimen; and   monitoring, using the EBSD detector, the resulting electrons emitted from the specimen at the plurality of locations and incident upon the scintillator member of the EBSD detector so as to obtain the first image data.   
     
     
         16 . The method according to  claim 15 , wherein the method further comprises causing the beam not to impinge upon the sample during a blanking period immediately prior to the monitoring period, wherein a duration of the blanking period is greater than or equal to a luminescence decay time period of the scintillator member, or wherein the electron beam is caused to impinge upon the plurality of locations according to a continuous scan pattern. 
     
     
         17 . A system for obtaining a modified image of a specimen in a scanning electron microscope, the system comprising:
 an electron backscatter diffraction, EBSD, detector and a processor,   the system being configured to:   acquire first image data, the first image data comprising a plurality of pixels having values representing monitored electrons emitted from the specimen, at a plurality of locations within a region thereof as a result of an electron beam of the scanning electron microscope impinging upon the plurality of locations, and incident upon a scintillator member of the EBSD detector; and   generate a modified image comprising a plurality of pixels each having a value calculated based on the value of a corresponding pixel of the first image data and an afterglow model representative of a luminescence persistence characteristic of the scintillator member.   
     
     
         18 . The system according to  claim 17 , wherein the system is configured such that:
 one or more virtual detector regions of the scintillator member may be defined,   whereby the first image data comprises, for each of the one or more virtual detector regions, a first image comprising a respective plurality of pixels, each pixel which corresponds to, and has a value representing the monitored electrons incident on the virtual detector region and emitted from, a location of the plurality of locations.   
     
     
         19 . A scanning electron microscope comprising the system according to  claim 17 . 
     
     
         20 . A computer program product comprising instructions which, when executed by a computer, cause the computer to carry out the method of  claim 1 .